ARC: [ASID] Track ASID allocation cycles/generations

This helps remove asid-to-mm reverse map

While mm->context.id contains the ASID assigned to a process, our ASID
allocator also used asid_mm_map[] reverse map. In a new allocation
cycle (mm->ASID >= @asid_cache), the Round Robin ASID allocator used this
to check if new @asid_cache belonged to some mm2 (from prev cycle).
If so, it could locate that mm using the ASID reverse map, and mark that
mm as unallocated ASID, to force it to refresh at the time of switch_mm()

However, for SMP, the reverse map has to be maintained per CPU, so
becomes 2 dimensional, hence got rid of it.

With reverse map gone, it is NOT possible to reach out to current
assignee. So we track the ASID allocation generation/cycle and
on every switch_mm(), check if the current generation of CPU ASID is
same as mm's ASID; If not it is refreshed.

(Based loosely on arch/sh implementation)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
index 88897a112d55..cf7d7d9ad695 100644
--- a/arch/arc/mm/tlbex.S
+++ b/arch/arc/mm/tlbex.S
@@ -140,12 +140,15 @@ ex_saved_reg1:
 	GET_CURR_TASK_ON_CPU  r3
 	ld r0, [r3, TASK_ACT_MM]
 	ld r0, [r0, MM_CTXT+MM_CTXT_ASID]
+	breq r0, 0, 55f	; Error if no ASID allocated
 
 	lr r1, [ARC_REG_PID]
 	and r1, r1, 0xFF
 
-	breq r1, r0, 5f
+	and r2, r0, 0xFF	; MMU PID bits only for comparison
+	breq r1, r2, 5f
 
+55:
 	; Error if H/w and S/w ASID don't match, but NOT if in kernel mode
 	lr  r2, [erstatus]
 	bbit0 r2, STATUS_U_BIT, 5f